Method and system for reducing particulate emissions

ABSTRACT

Methods and systems are provided for filtering particulate matter in an exhaust passage of an engine system. In one example, a method may include during a cold start condition comprising an engine temperature being less than a threshold engine temperature, directing engine exhaust gas to an exhaust particulate filter, and during a warm engine condition, directing engine exhaust gas to bypass the exhaust particulate filter, wherein the warm engine condition comprises the engine temperature being greater than or equal to the threshold engine temperature and fuel being combusted in the engine. In this way, the exhaust particulate filter may be reliably regenerated during engine shutdown events such as DFSOs while reducing filter degradation, and lowering PM emissions.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 15/041,689, entitled “METHOD AND SYSTEM FOR REDUCING PARTICULATEEMISSIONS,” filed on Feb. 11, 2016. The entire contents of theabove-referenced application are hereby incorporated by reference in itsentirety for all purposes.

FIELD

The present description relates generally to the design and use of anengine exhaust system for reducing particulate emissions from acombustion engine.

BACKGROUND/SUMMARY

Engine combustion using diesel or gasoline fuel may generate particulatematter (PM) (such as soot and aerosols) that can be exhausted to theatmosphere. To enable emissions compliance, particulate filters such asdiesel particulate filters (DPFs) and gasoline particulate filters(GPFs) may be included inline in the engine exhaust stream, to filterout exhaust PMs before releasing the exhaust. Particulate filters thatbecome clogged with PM may be regenerated in-situ during decelerationfuel shut off (DFSO) events by supplying excess oxygen to the filter andraising the filter temperature to oxidize the PM. One example approachshown by Bidner et. al. in U.S. Pat. No. 8,424,295 discloses increasingexcess oxygen to the particulate filter during engine shutdownconditions and regenerating the particulate filter at least during aportion of the engine shutdown.

However, the inventors herein have recognized potential disadvantageswith the above approach. Oxygen flow to the filter during DFSO or otherengine shutdown events may increase the filter temperature excessivelyleading to premature filter degradation. Furthermore, employingstrategies to limit DFSO duration to mitigate excessive exhaustparticulate filter temperature increases and premature filterdegradation can reduce fuel economy, and may also reduce drivability.Further still during short engine on periods (e.g., during short vehicletrips), the particulate filter temperature may fail to reach a highenough temperature for regeneration.

The inventors herein have identified an approach that at least partlyaddresses the above issues. In one example, a method for a combustionengine may comprise: during a cold start condition comprising an enginetemperature being less than a threshold engine temperature, directingengine exhaust gas to an exhaust particulate filter; and during a warmengine condition, directing engine exhaust gas to bypass the exhaustparticulate filter, wherein the warm engine condition comprises theengine temperature being greater than or equal to the threshold enginetemperature and fuel being combusted in the engine.

In another example, a method may comprise: in response to an enginetemperature being greater than a threshold engine temperature, directingexhaust gas to bypass an exhaust particulate filter during engine fuelcombustion, and heating the exhaust particulate filter when an exhaustparticulate filter temperature decreases below a threshold filtertemperature; and in response to an engine temperature being less than athreshold engine temperature, directing exhaust gas to the exhaustparticulate filter and ceasing to heat the exhaust particulate filter.

In a further example, an engine system may comprise: an engine; anexhaust particulate filter positioned in an exhaust bypass passagedownstream of the engine; an exhaust diverter valve positioned upstreamof the exhaust bypass passage; and a controller, including executableinstructions to, during a first condition comprising an enginetemperature being less than a threshold engine temperature, positioningthe exhaust diverter valve to direct engine exhaust gas to the exhaustbypass passage and the exhaust particulate filter; and during a secondcondition, positioning the exhaust diverter valve to direct engineexhaust gas to bypass the exhaust bypass passage, wherein the secondcondition comprises the engine temperature being greater than or equalto the threshold engine temperature and fuel being combusted in theengine.

In this way, the technical effect may be achieved that the exhaustparticulate filter may be reliably regenerated during engine shutdownevents such as DFSOs without premature degradation. Furthermore, byavoiding any limiting of the engine shutdown events, drivability andfuel economy are maintained. Further still, by diverting the exhauststream to the exhaust particulate filter during engine cold startconditions and bypassing the exhaust particulate filter during warmengine combustion conditions, the exhaust particulate filter size may bereduced thereby lowering manufacturing costs and improving reliabilitywhile maintaining vehicle PM emissions. Further still, by heating theexhaust particulate filter during warm engine conditions and duringengine fuel combustion, the exhaust particulate filter temperature canbe preheated to a temperature high enough for filter regeneration.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example engine system including an exhaust particulatefilter positioned downstream of an emissions control device.

FIG. 2 shows a plot of cumulative particulate matter generation from avehicle testing under a New European Driving Cycle (NEDC).

FIGS. 3 and 4 show example exhaust systems of the engine system of FIG.1, including an exhaust diverter valve and an exhaust particulatefilter.

FIG. 5 shows a flow chart for an example method of operating an enginesystem, including an exhaust diverter valve and an exhaust particulatefilter.

FIG. 6 shows an example timeline illustrating operation of an enginesystem, including an exhaust diverter valve and an exhaust particulatefilter.

DETAILED DESCRIPTION

The following description relates to systems and methods for reducingparticulate emissions from an engine system including an exhaustdiverter valve and an exhaust particulate filter. A vehicle enginesystem, including an exhaust particulate filter, may be configured tooperate with fuels such as diesel or gasoline is shown in FIG. 1. Theexhaust particulate filter may include a diesel particulate filter(DPF), a gasoline particulate filter (GPF), and the like, to filterparticulate matter (PM) in the engine exhaust. The exhaust particulatefilter may capture PM during vehicle driving, as illustrated by the plotin FIG. 2. As shown in FIGS. 3-4, the exhaust may be directed to anexhaust particulate filter disposed in a bypass exhaust passage via anexhaust diverter valve in the main exhaust passage. A method foroperating the engine system, including the exhaust diverter valve fordirecting exhaust to the exhaust particulate filter is shown in FIG. 5.FIG. 6 illustrates an example timeline for operating an engine systemvia the method of FIG. 5. In this way, vehicle emissions may be reducedwhile maintaining fuel economy, vehicle drivability, and engine systemreliability.

FIG. 1 is a schematic diagram showing one cylinder of a multi-cylinderengine 10 in an engine system 100, which may be included in a propulsionsystem of a vehicle. The engine 10 may be controlled at least partiallyby a control system including a controller 12 and by input from avehicle operator 132 via an input device 130. In this example, the inputdevice 130 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal. A combustionchamber 30 of the engine 10 includes a cylinder formed by cylinder walls32 with a piston 36 positioned therein. The piston 36 may be coupled toa crankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. The crankshaft 40 may becoupled to at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled to thecrankshaft 40 via a flywheel to enable a starting operation of theengine 10.

The combustion chamber 30 may receive intake air from an intake manifold44 via an intake passage 42 and may exhaust combustion gases via anexhaust passage (e.g., exhaust pipe) 48. The intake manifold 44 and theexhaust passage 48 (e.g., exhaust main passage) can selectivelycommunicate with the combustion chamber 30 via respective intake valve52 and exhaust valve 54. In some examples, the combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

In this example, the intake valve 52 and exhaust valve 54 may becontrolled by cam actuation via respective cam actuation systems 51 and53. The cam actuation systems 51 and 53 may each include one or morecams and may utilize one or more of cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by the controller 12 tovary valve operation. The position of the intake valve 52 and exhaustvalve 54 may be determined by position sensors 55 and 57, respectively.In alternative examples, the intake valve 52 and/or exhaust valve 54 maybe controlled by electric valve actuation. For example, the cylinder 30may alternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT systems.

A fuel injector 69 is shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofa signal received from the controller 12. In this manner, the fuelinjector 69 provides what is known as direct injection of fuel into thecombustion chamber 30. The fuel injector may be mounted in the side ofthe combustion chamber (as shown) or in the top of the combustionchamber, for example. Fuel may be delivered to the fuel injector 69 by afuel system (not shown) including a fuel tank, one or more fuel pumps,and a fuel rail. In some examples, the combustion chamber 30 mayalternatively or additionally include a fuel injector arranged in theintake manifold 44 in a configuration that provides what is known asport injection of fuel into the intake port upstream of the combustionchamber 30. Fuel injection flow rates may be estimated and/or measuredby the fuel pump rates to the fuel injectors. The fuel may comprisegasoline, diesel, ethanol blends, biodiesel, and a combination thereof.

Spark is provided to combustion chamber 30 via spark plug 66. Theignition system may further comprise an ignition coil (not shown) forincreasing voltage supplied to spark plug 66. In other examples, such asa diesel engine, spark plug 66 may be omitted.

The intake passage 42 may include a throttle 62 having a throttle plate64. In this particular example, the position of throttle plate 64 may bevaried by the controller 12 via a signal provided to an electric motoror actuator included with the throttle 62, a configuration that iscommonly referred to as electronic throttle control (ETC). In thismanner, the throttle 62 may be operated to vary the intake air providedto the combustion chamber 30 among other engine cylinders. The positionof the throttle plate 64 may be provided to the controller 12 by athrottle position signal. The intake passage 42 may include a mass airflow sensor 120 and a manifold air pressure sensor 122 for sensing anamount of air entering engine 10.

An exhaust gas sensor 126 is shown coupled to the exhaust passage 48upstream of both an exhaust gas recirculation system 140 and an emissioncontrol device 70 according to a direction of exhaust flow. The sensor126 may be any suitable sensor for providing an indication of exhaustgas air-fuel ratio such as a linear oxygen sensor or UEGO (universal orwide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO(heated EGO), a NO_(x), HC, or CO sensor. In one example, upstreamexhaust gas sensor 126 is UEGO configured to provide output, such as avoltage signal, that is proportional to the amount of oxygen present inthe exhaust. Controller 12 converts oxygen sensor output into exhaustgas air-fuel ratio via an oxygen sensor transfer function.

An exhaust gas recirculation (EGR) system 140 may route a desiredportion of exhaust gas from the exhaust passage 48 to the intakemanifold 44 via an EGR passage 152. The amount of EGR provided to theintake manifold 44 may be varied by the controller 12 via an EGR valve144. Under some conditions, the EGR system 140 may be used to regulatethe temperature of the air-fuel mixture within the combustion chamber,thus providing a method of controlling the timing of ignition duringsome combustion modes.

The emission control device 70 is shown arranged along the exhaustpassage 48 downstream of the exhaust gas sensor 126. The emissioncontrol device 70 may be a three way catalyst (TWC), NO_(x) trap,various other emission control devices, or combinations thereof. In someexamples, during operation of the engine 10, the emission control device70 may be periodically reset by operating at least one cylinder of theengine within a particular air-fuel ratio.

A particulate filter 72 is shown arranged along an exhaust bypasspassage 82 off of the exhaust passage 48 downstream of the emissioncontrol device 70. As shown in FIG. 1, an exhaust diverter valve 80 maybe positioned in the main exhaust passage 48 at the inlet junction ofthe exhaust bypass passage 82. As such, the exhaust diverter valve 80may be positioned, either to divert exhaust gas from the main exhaustpassage 48 to the exhaust bypass passage 82 and the exhaust particulatefilter 72, or to bypass the exhaust bypass passage 82 and the exhaustparticulate filter 72. Controller 12 may control actuation of theexhaust diverter valve 80. Although not shown in FIG. 1, a check valvemay be positioned downstream of the exhaust particulate filter 72 withinthe exhaust bypass passage 82 to prevent flow of exhaust gasesdownstream from the exhaust particulate filter 72 in the main exhaustpassage 48 back to the exhaust bypass passage 82. A particulate filtertemperature sensor 76 may also be positioned at or in the vicinity ofexhaust particulate filter 72 to estimate the particulate filtertemperature. Furthermore, a particulate filter heater 78 may bethermally coupled to the exhaust particulate filter 72. Particulatefilter heater may be controlled by controller 12 for preheating theparticulate filter 72 prior to regeneration of the particulate filter.

The exhaust gas treated by emission control device 70 and particulatefilter 72 is released into the atmosphere through tailpipe 86. Theparticulate filter 72 may be a diesel particulate filter, a gasolineparticulate filter, and the like. A substrate of the particulate filter72 may be made of ceramic, silicon, metal, paper, or combinationsthereof. During operation of the engine 10, particulate filter 72 maycapture exhaust particulate matter (PMs), such as ash and soot (e.g.,from unburned hydrocarbons) in order to reduce vehicle emissions. Thesoot may clog the surfaces of the particulate filter thereby creating anexhaust backpressure. The exhaust backpressure may negatively influencethe engine performance. Once the particulate filter 72 becomes fullyloaded with soot (e.g., soot load on the particulate filter exceeds asoot load threshold), the backpressure may be too high for properexhaust expulsion. Work used to expel exhaust from the engine 10increases in order to overcome the backpressure described above. Inorder to avoid high backpressure, an engine 10 may periodicallyregenerate the filter either passively or actively.

The pressure drop across the filter may measured by one or more pressuresensors 74 located at or in the vicinity of the particulate filter 72.As an example, the one or more pressure sensors may be positionedimmediately upstream and immediately downstream from the particulatefilter 72 within exhaust bypass passage 82. In other examples, the oneor more pressure sensors may be positioned at other locations within themain exhaust passage 48 or exhaust bypass passage 82. As an example, theparticulate filter may be regenerated in response to a pressure dropacross the particulate filter 72 increasing above a threshold filterpressure drop.

Passive regeneration may occur when an engine load exceeds a thresholdload causing an exhaust temperature to rise. As the exhaust temperatureincreases beyond a threshold temperature (e.g., 450° C.), the soot onthe particulate filter 72 may combust. Therefore, passive regenerationoccurs without alterations to engine operations. Conversely, activeregeneration occurs via the controller 12 signaling for alterations toengine operations in order to increase exhaust temperatures (e.g., lateinjection, secondary injection, throttling, exhaust recirculation, sparkretard, and/or a decrease in air/fuel ratio) independent of the engineload. For example, the controller may send signals to a fuel injector todecrease the pulse-width of the fuel injection, and lean the combustionair-fuel ratio (relative to stoichiometry). As another example, thecontroller may send signals to an electromechanical actuator coupled tothe intake throttle to move the throttle valve towards a more openposition, thereby increasing airflow to the engine. In still otherexamples, valve timing may be adjusted (e.g., via cam adjustments) toincrease positive valve overlap. Further still, the controller mayposition exhaust diverter valve to direct exhaust gas to the exhaustbypass passage 82 and the exhaust particulate filter 72 duringdeceleration fuel shut-off (DFSO) or other engine shutdown events toactively regenerate the exhaust particulate filter 72. Further still,the controller 12 may preheat the exhaust particulate filter 72 to athreshold particulate filter temperature using an exhaust particulatefilter heater 78 thermally coupled to the exhaust particulate filterprior to active regeneration. When the exhaust particulate filter isclogged the controller may send a message to the vehicle operatorindicating regeneration of the exhaust particulate filter is to beconducted. As described above, active regeneration may include retardingthe engine spark timing to increase engine air flow and subsequentlyincrease exhaust particulate filter temperature.

As the soot burns during either passive or active regeneration, theparticulate filter temperature increases to a higher temperature (e.g.,1400° C.). Extended engine operation at the elevated regenerationtemperature may expedite degradation of the particulate filter 72.Degradation may include the particulate filter 72 developing a leak(e.g., crack) and/or a hole, which may cause soot to escape from thefilter, and flow further downstream into the exhaust passage 48,increasing vehicle emissions. As such, this can cause an engine to beemissions non-compliant.

Other factors contributing to particulate filter degradation includevehicle vibrations and lubricating oil ash. Vehicle vibrations maydegrade fragile components within the particulate filter 72 due toexpansion of the components (e.g., decreased stability) caused byexposure of the particulate filter 72 to high temperatures. Lubricatingoil ash may contain metal oxides which can react with the particulatefilter 72 and form phases (e.g., portions of the particulate filterdegrade while other portions remain functional), ultimately degrading atleast a portion of the particulate filter.

The controller 12 is shown in FIG. 1 as a microcomputer, including amicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 (e.g., non-transitory memory) in this particularexample, random access memory 108, keep alive memory 110, and a databus. The controller 12 may receive various signals from sensors coupledto the engine 10, in addition to those signals previously discussed,including measurement of inducted mass air flow (MAF) from the mass airflow sensor 120; engine coolant temperature (ECT) from a temperaturesensor 112 coupled to a cooling sleeve 114; an engine position signalfrom a Hall effect sensor 118 (or other type) sensing a position ofcrankshaft 40; throttle position from a throttle position sensor 65; andmanifold absolute pressure (MAP) signal from the sensor 122. An enginespeed signal may be generated by the controller 12 from crankshaftposition sensor 118. Manifold pressure signal also provides anindication of vacuum, or pressure, in the intake manifold 44. Note thatvarious combinations of the above sensors may be used, such as a MAFsensor without a MAP sensor, or vice versa. During engine operation,engine torque may be inferred from the output of MAP sensor 122 andengine speed. Further, this sensor, along with the detected enginespeed, may be a basis for estimating charge (including air) inductedinto the cylinder. In one example, the crankshaft position sensor 118,which is also used as an engine speed sensor, may produce apredetermined number of equally spaced pulses every revolution of thecrankshaft.

The storage medium read-only memory 106 can be programmed with computerreadable data representing non-transitory instructions executable by theprocessor 102 for performing the methods described below as well asother variants that are anticipated but not specifically listed.

The controller 12 receives signals from the various sensors of FIG. 1and employs the various actuators of FIG. 1 to adjust engine operationbased on the received signals and instructions stored on a memory of thecontroller 12. As described above, the controller may employ actuatorssuch as the exhaust particulate filter heater 78 and the exhaustdiverter valve 80 based on received signals from one or more pressuresensors 74, temperature sensors 76, and other engine system sensors. Forexample, the controller may also actuate the exhaust particulate filterheater 78 and the exhaust diverter valve based on signals received froman engine temperature sensor (such as ECT sensor 112), and one or morefuel pumps, such as the fuel pump flow rate or the fuel injection flowrate.

Turning now to FIG. 2, it illustrates an example plot 200 showingcumulative PM generation from a combustion engine resulting from a newEuropean driving cycle (NEDC) test. Plot 200 illustrates that a majorfraction of the overall PM generation occurs during the cold startperiod indicated prior to dashed boundary line 220. During the coldstart period, when the engine temperature is low (e.g., cold), fuelcombustion quality in a combustion engine may be low or incomplete,giving rise to a higher level of PM. As such, diverting exhaust gases toan exhaust particulate filter to capture PM generated during cold startconditions may significantly reduce engine PM emissions.

Turning now to FIG. 3, it illustrates an example engine exhaust system300 of the engine system 100 shown in FIG. 1. Exhaust from the engineflows from main exhaust passage 48 through ECD 70 to exhaust passage 348immediately upstream from exhaust bypass passage 82. As shown in FIG. 3,controller 12 may position exhaust diverter valve 80 to divert exhaustgas from the exhaust passage 348 to the exhaust bypass passage 82 whereit may be filtered by the exhaust particulate filter 72. Alternately,controller 12 may move exhaust diverter valve 80 in the direction ofarrow 380 so that the exhaust gas in exhaust passage 348 bypasses theexhaust particulate filter 72 and continues along exhaust passage 348 tothe tail pipe. As described above, a check valve may be positioned inthe portion of the exhaust bypass passage 382 downstream from theexhaust particulate filter 72 in order to prevent backflow of exhaustgases from the exhaust passage 348 to the exhaust bypass passage 382. Insome examples, the exhaust bypass passage 82 (including 382) may besmaller than the main exhaust passage 48, whereby a cross-sectional areaor diameter of the exhaust bypass passage 82 is less than across-sectional area or diameter of the main exhaust passage 48.Controller 12 may also actuate exhaust particulate filter heater 78,which is thermally coupled to the exhaust particulate filter 72, toraise the temperature of the exhaust particulate filter above athreshold filter temperature prior to regeneration of the exhaustparticulate filter 72. Exhaust particulate filter heater may include anelectrically powered coiled element heater that is partially or entirelywrapped around the external surface of the body of the exhaustparticulate filter 72, or other types of heaters.

During cold start conditions, the exhaust diverter valve 80 may bepositioned to divert exhaust gases from the main exhaust passage 48 toexhaust bypass passage 82 and the exhaust particulate filter 72. In thisway, a substantial portion of the particulate matter generated from fuelcombustion in the engine may be filtered by the exhaust particulatefilter 72, thereby maintaining or reducing PM emissions. Cold startconditions may include the engine status being ON, and the enginetemperature, such as the ECT measured by temperature sensor 112 beingless than a threshold engine temperature. The threshold enginetemperature may correspond to a temperature above which PM generated bycombustion of fuel in the engine is significantly reduced or near zero.As other examples, the engine temperature may correspond to an engineoil temperature, an engine block temperature, an engine exhausttemperature, and the like. Furthermore, the cold start condition mayalternatively comprise a plurality of such engine temperatures beingless than a plurality of corresponding threshold engine temperatures.Additionally, the cold start condition may include a duration after anengine status is switched from OFF to ON when the engine temperature isless than the threshold engine temperature being greater than athreshold duration.

During warm engine conditions, including when an engine temperature,such as the ECT measured by temperature sensor 112, is greater than thethreshold engine temperature, the exhaust diverter valve 80 may bepositioned indicated by arrow 380 so that exhaust gas bypasses theexhaust particulate filter 72 during engine combustion conditions. Theengine temperature may include a cylinder head temperature (CHT) and thethreshold engine temperature may include a threshold CHT. In otherexamples, warm engine conditions (or departure from cold startconditions) may be determined by an elapsed engine ON duration from anengine start increasing above a threshold duration. Warm engineconditions may further be determined via an inferred piston temperaturemodel on-board the controller. In other examples warm engine conditionsmay be determined by transition from a first fuel injection mode to asecond fuel injection mode in a split mode fuel injection engineoperation. In yet another example, warm engine conditions may bedetermined by an emissions control device (ECD) catalyst heating mode.For example, during cold start conditions, the ECD catalyst may berapidly heated in order to reduce engine emissions. Conversely, duringwarm engine conditions, the rapid heating of the ECD catalyst may beswitched off. Thus the warm engine conditions may be indicated by theECD catalyst heating mode being switched off. Engine combustionconditions may be determined by a fuel injection flow rate to the enginebeing greater than a threshold fuel injection flow rate. As describedabove, the fuel injection flow rate may be estimated or determined froma pump rate of one or more fuel pumps in the engine fuel system.Alternately, engine combustion conditions may be determined by thedelivery of a spark to combustion chamber 30 via spark plug 66 while thefuel injection flow rate is greater than a threshold fuel injection flowrate. In one example, delivery of a spark to the combustion chamber 30may be indicated by the supply of power to the ignition systemcomprising an ignition coil (not shown) for increasing voltage suppliedto spark plug 66. Thus, engine combustion conditions may be indicated ifa voltage supplied to spark plug 66 is greater than a threshold voltageand the fuel injection flow rate is greater than the threshold fuelinjection flow rate. In another example, engine combustion may bedetected via crankshaft acceleration increasing above a thresholdcrankshaft acceleration. The crankshaft acceleration may be measured viaa crankshaft position (CKP) sensor such as Hall effect position sensor118, and the threshold crankshaft acceleration may correspond to acrankshaft acceleration above which combustion in the engine isindicated.

When fuel combustion occurs during warm engine conditions, the amount ofPM generated by the engine may be very low as compared to PM generatedduring cold start conditions. Accordingly, in response to the enginetemperature increasing above a threshold engine temperature and inresponse to indication of fuel combustion conditions, the exhaustdiverter valve may be positioned to direct exhaust gas to bypass theexhaust particulate filter 72, while maintaining PM emissions.Accordingly, combusted exhaust gas (e.g., engine exhaust gas resultingfrom fuel combustion in the engine) may only be directed to the exhaustbypass passage and the exhaust particulate filter 72 during cold startconditions. During warm engine conditions, when an engine temperature isgreater than a threshold engine temperature, the exhaust diverter valvemay be positioned to direct the combusted exhaust gas to bypass theexhaust particulate filter 72 positioned in the exhaust bypass passage82. Accordingly, during engine combustion events outside of the coldstart conditions, engine exhaust (combusted exhaust) may be directed tobypass the exhaust particulate filter 72. Furthermore, in some examples,the engine exhaust system may further comprise a second exhaustparticulate filter positioned at ECD 70, to capture the auxiliary PMgenerated during fuel combustion under warm engine conditions.

Although the exhaust diverter valve 80 may be positioned to directexhaust gas to bypass the exhaust particulate filter 72, controller 12may switch on exhaust particulate filter heater 78 to heat the exhaustparticulate filter 72 during warm engine conditions and fuel combustionconditions. The exhaust particulate filter heater 78 may comprise anelectrically powered or other type of heater thermally coupled to theexhaust particulate filter 72. In the example exhaust system 400 of FIG.4, heating the exhaust particulate filter 72 may comprise positioningthe exhaust particulate filter 72 directly adjacent to ECD 70 such thatexhaust particulate filter 72 is thermally coupled to ECD 70 viathermally conductive surface 472. Heating the exhaust particulate filter72 during warm engine and fuel combustion conditions may allow forpreheating of the exhaust particulate filter 72 to a threshold filtertemperature prior to regeneration. Preheating the exhaust particulatefilter 72 to the threshold filter temperature may help to ensure thatthe exhaust particulate filter 72 can be promptly regenerated when theexhaust particulate filter becomes clogged, for example, when an exhaustparticulate filter pressure across the filter is greater than athreshold filter pressure drop. In one example, the threshold filtertemperature may be approximately 500° C. (e.g., above the thresholdtemperature of 450° C., at which soot combusts). For example, when theexhaust particulate filter is above the threshold filter temperature,directing exhaust oxygen to the exhaust particulate filter may oxidizeand combust the soot particles contained therein, thereby regeneratingthe exhaust particulate filter. If the exhaust particulate filtertemperature is below the threshold filter temperature, the thermalenergy contained in the exhaust particulate filter may be insufficientto fully or partially regenerate the exhaust particulate filter 72 whenexhaust oxygen is directed to the filter. In response to the exhaustparticulate filter temperature increasing above the threshold filtertemperature, the controller 12 may switch the exhaust particulate filterheater 78 OFF. Accordingly, during engine combustion events outside ofthe cold start conditions, engine exhaust (combusted exhaust) may bedirected to bypass the exhaust particulate filter 72 and the exhaustparticulate filter 72 may be selectively electrically heated via theexhaust particulate filter heater 78. Furthermore, when the exhaustparticulate filter temperature is heated above the threshold filtertemperature, uncombusted exhaust gas (engine exhaust during engineshutdown conditions such as DFSO conditions) may be directed to theexhaust bypass passage 82 to regenerate the exhaust particulate filter72.

The controller 12 may initiate regeneration of the exhaust particulatefilter 72 during warm engine conditions outside of fuel combustionconditions. Warm engine conditions outside of fuel combustion conditionsmay occur when the engine is switched OFF after being on for a duration.For example, the engine may be switched OFF during DFSO events or for ahybrid vehicle when operating in electric-only mode (e.g., the hybridvehicle is propelled by the electric motor but not by the engine).Furthermore, controller 12 may initiate regeneration of the exhaustparticulate filter during warm engine conditions outside of fuelcombustion conditions when the exhaust particulate filter temperature isgreater than a threshold filter temperature. Further still, thecontroller 12 may initiate regeneration of the exhaust particulatefilter during warm engine conditions outside of fuel combustionconditions when the exhaust particulate filter temperature is greaterthan the threshold filter temperature and when the exhaust particulatefilter pressure drop is greater than a threshold filter pressure drop.Initiating regeneration of the exhaust particulate filter may comprisepositioning the exhaust diverter valve 80 to direct exhaust to flow tothe exhaust bypass passage 82 and the exhaust particulate filter 72.During warm engine conditions outside of fuel combustion conditions(e.g., engine OFF conditions, DFSO conditions), fuel is not combustedinside the engine and the exhaust gas may largely contain air, includingoxygen. As described above, when the exhaust particulate filtertemperature is above the threshold filter temperature, flowing exhaustoxygen through the filter may oxidize and combust soot PM containedtherein, thereby regenerating the exhaust particulate filter.

During filter regeneration, the pressure drop across the exhaustparticulate filter 72 may decrease as soot PM contained therein areoxidized and combusted. As described above, filter regeneration may beinitiated at least partially in response to engine operating conditionsincluding the pressure drop across the exhaust particulate filterincreasing above a threshold pressure drop. Accordingly, in response tothe pressure drop across the exhaust particulate filter decreasing belowthe threshold pressure drop, filter regeneration may be stopped by thecontroller 12. Terminating filter regeneration may include positioningthe exhaust diverter valve to direct exhaust gas to bypass the exhaustparticulate filter. As described above, filter regeneration occursduring warm engine conditions outside of fuel combustion in the engine.Consequently, directing exhaust gas to bypass the exhaust particulatefilter and to pass through the exhaust passage 48, ECD 70, and exhaustpassage 348 to the tailpipe may not substantially increase PM emissions.Furthermore, should the engine temperature decrease below the thresholdengine temperature after terminating the filter regeneration, thecontroller 12, in response, may reposition the exhaust diverter valve 80to direct exhaust gas to flow through the exhaust bypass passage 82 andthe exhaust particulate filter 72, thereby reducing PM emissions.

As described above, being positioned in the exhaust bypass passage 82allows for the exhaust particulate filter 72 to be used to filter PM inthe exhaust gas selectively during cold start conditions. As such, thesizing of the exhaust particulate filter 72 may be smaller thanconventional exhaust particulate filters. Conventional exhaustparticulate filters, such as DPFs and GPFs that are positioned in themain exhaust passage, filter all the exhaust gas from the engine.Conventional exhaust particulate filters are exposed to other types ofparticles other than soot PM, including larger inert particles such asrust, upstream catalyst fragment particles, metal particles, and thelike. These larger inert particles may not be oxidized or combustedduring filter regeneration and thus can steadily accumulate in anddegrade particulate filters. By positioning the exhaust particulatefilter 72 in the bypass exhaust passage, and by selectively flowingexhaust gas to the exhaust particulate filter 72 during cold startconditions and for filter regeneration, as described above, the amountof larger inert particles encountering the exhaust particulate filter 72may be substantially reduced. Accordingly, the sizing of the exhaustparticulate filter can be smaller, and the frequency and effectivenessof regenerations thereof can be higher, thus decreasing vehiclemanufacturing and operating costs and increasing vehicle reliability.

The power of the exhaust particulate filter heater 78 may besubstantially less than a conventional electrical heater employed forelectrically heating conventional emission control devices such as a TWCfor hydrocarbon reduction. For example, whereas conventional heaterstypically consume greater than 2.2 kW of power, the exhaust particulatefilter heater 78 may consume a much smaller amount of power, forexample, 75 W. The exhaust particulate filter heater 78 may be dedicatedfor heating the exhaust particulate filter 72 and so may be smaller insize and may consume less power than conventional ECD heaters, which maybe used for heating catalyst bricks integrated with other additional ECDdevices such as particulate filters, housings, and the like.Furthermore, as described above, the exhaust particulate filter 72 ispositioned in the exhaust bypass passage 82, and may be sizedsubstantially smaller than conventional particulate filters that arepositioned in the main exhaust passage 48 (which is larger incross-sectional area than the exhaust bypass passage 82). Furthermore,the exhaust particulate filter heater 78 may be smaller thanconventional ECD heaters because the exhaust particulate filter 72 ispositioned in the exhaust bypass passage 82 and may be bypassed duringengine operating conditions where PM is lower; in other words, thefilter load, and consequently the regeneration frequency, of the exhaustparticulate filter may be reduced. In one example, the exhaustparticulate filter may comprise a mini-particulate filter, havingapproximate dimensions of the exhaust particulate filter 72 may comprisea diameter <30 mm, a length <205 mm, a cross sectional area <1 squareinch, and a ceramic volume of <50000 mm³. Furthermore, the mass ofceramic material contained within the filter may be <65 g. The exhaustparticulate filter size may vary according to engine displacement, sootoutput, and maximum soot load threshold. Further still, the exhaustparticulate filter 72 may comprise a thermally insulated filter so thatthermal energy losses from the exhaust particulate filter 72 arereduced, and so that the power consumed to heat the exhaust particulatefilter 72 is reduced. Thermally insulating the exhaust particulatefilter 72 may comprise thermally insulating external surfaces of theexhaust particulate filter 72 with an insulating, non-flammablematerial.

Turning now to FIG. 4, it illustrates another example configuration ofan exhaust system 400 of engine system 100. Exhaust system 400 may beoperated as part of engine system 100 similarly to exhaust system 300 asdescribed above with reference to FIG. 3. However, in the exhaust system400, exhaust bypass passage 82 and exhaust particulate filter 72 arearranged such that the exhaust particulate filter 72 is thermallycoupled to the ECD 70 via at least one common thermally conductivesurface 472. In this way, thermal energy from ECD 70 may be conducted ortransferred via thermally conductive surface 472 to heat exhaustparticulate filter 72, thus further lowering the amount heating poweroutput from exhaust particulate filter heater 78 for raising thetemperature of the exhaust particulate filter 72 to a threshold filtertemperature prior to filter regeneration. ECD 70 may be heated at leastpartially from the hot engine exhaust gases passing therethrough.Furthermore, an ECD heater may be employed and controlled by controller12 to heat ECD 70. In the case where the exhaust bypass passage 82 andexhaust particulate filter 72 are arranged such that the exhaustparticulate filter 72 is thermally coupled to the ECD 70 via at leastone common thermally conductive surface 472, all external surfaces ofthe exhaust particulate filter 72 may be thermally insulated except forthe common thermally conductive surface 472.

Positioning the exhaust particulate filter 72 downstream from ECD 70(including a catalyst such as a TWC, NOx reduction catalyst, and thelike) may further be used to increase backpressure in the main exhaustpassage 48 for increasing ECD temperatures during cold start conditions,even though PM levels in the exhaust may be low during cold startconditions. In this way, power consumed to heat the catalyst may bereduced and the catalyst may be preheated more rapidly, therebyincreasing fuel economy and reducing exhaust emissions.

In this manner, an engine system may comprise: an engine; an exhaustparticulate filter positioned in an exhaust bypass passage downstream ofthe engine; an exhaust diverter valve positioned an exhaust divertervalve positioned in an exhaust main passage upstream of the exhaustbypass passage upstream of the exhaust bypass passage; and a controller,including executable instructions to, during a first conditioncomprising an engine temperature being less than a threshold enginetemperature, positioning the exhaust diverter valve to direct engineexhaust gas from the exhaust main passage to the exhaust bypass passageand the exhaust particulate filter; and during a second condition,positioning the exhaust diverter valve to direct engine exhaust gas tobypass the exhaust bypass passage, wherein the second conditioncomprises the engine temperature being greater than or equal to thethreshold engine temperature and fuel being combusted in the engine.Additionally or alternatively, the engine system may further comprise anexhaust particulate filter heater, wherein the executable instructionsfurther comprise heating the exhaust particulate filter to aregeneration temperature with the exhaust particulate filter heaterduring the second condition. Additionally or alternatively, the exhaustparticulate filter heater comprises an electrical heating elementthermally coupled to the exhaust particulate filter. Additionally oralternatively, the exhaust particulate filter heater may comprise anemission control device upstream of the exhaust particulate filter andthermally coupled to the exhaust particulate filter, and heating theexhaust particulate filter may comprise during the second condition,transferring thermal energy from the emission control device to theexhaust particulate filter. Additionally or alternatively, theexecutable instructions may further comprise during a third condition,positioning the exhaust diverter valve to direct engine exhaust gas tothe exhaust bypass passage and the exhaust particulate filter, whereinthe third condition comprises a fuel injection flow rate being less thana threshold flow while the engine temperature is greater than thethreshold engine temperature. Additionally or alternatively, the thirdcondition may further comprise the exhaust particulate filtertemperature being greater than the regeneration temperature.Additionally or alternatively, the third condition may further comprisean exhaust particulate filter pressure drop being greater than athreshold pressure drop. Additionally or alternatively, the executableinstructions may further comprise, during the third condition, inresponse to the exhaust particulate filter pressure drop decreasingbelow the threshold pressure drop, positioning the exhaust divertervalve to direct engine exhaust to bypass the exhaust bypass passage.Additionally or alternatively, the executable instructions may furthercomprise, during the third condition, in response to the exhaustparticulate filter temperature decreasing below the regenerationtemperature, positioning the exhaust diverter valve to direct engineexhaust to bypass the exhaust bypass passage. Additionally oralternatively, a cross-sectional area of the exhaust bypass passage issmaller than a cross-sectional area of the exhaust main passage.

Turning now to FIG. 5, it illustrates a flow chart for an example method500 of operating an engine system, including an exhaust diverter valveand an exhaust particulate filter positioned in an exhaust bypasspassage and thermally coupled to an exhaust particulate filter heater.Method 500 may be executed as executable instructions on board a vehiclecontroller, such as controller 12. Method 500 begins at 502 where enginesystem conditions such as vehicle speed (Vs), engine rpm, engine coolanttemperature (ECT), fuel injection flow rate (Q_(inj)), and the like, areestimated and/or measured by the controller.

At 510, the controller may determine if engine cold start conditionshave been met. Engine cold start conditions may include an enginetemperature, T_(engine), being less than a threshold engine temperature,T_(engine,TH). As described above, T_(engine) may comprise ECT, engineoil temperature, engine block temperature, engine exhaust temperature,or another temperature indicative of the engine operating temperature,or a combination thereof. T_(engine,TH) may represent a temperaturebelow which combustion of fuel in the engine is more incomplete or ofpoorer quality such that a substantially higher amount of PM is emittedin the engine exhaust. Conversely, when T_(engine)>T_(engine,TH),combustion of fuel in the engine is more complete or of higher qualitysuch that a substantially lower amount of PM is emitted in the engineexhaust.

If the cold start conditions are met, method 500 proceeds to 514 wherethe controller may position the exhaust diverter valve 80 to divertexhaust gas to the exhaust particulate filter 72 via exhaust bypasspassage 82. By directing exhaust gas to the exhaust particulate filter72, PM generated by fuel combustion during cold start conditions may befiltered from the exhaust gas and PM emissions may be reduced. At 518,controller 12 may turn off the exhaust particulate filter heater 78 tostop heating of the exhaust particulate filter 72. After 518, method 500ends.

Returning to 510, if the cold start conditions are not met, method 500continues at 520 where controller 12 may determine if the engine isoperating outside of fuel combustion conditions. As described above, theengine may be operating outside of fuel combustion conditions if thefuel injection flow rate, Q_(inj), is less than a threshold fuelinjection flow rate, Q_(inj,TH). Fuel injection flow rate may beestimated or measured by a fuel pump flow rate of one or more fuel pumpsof the engine fuel system. Alternately, the engine may be operatingoutside of fuel combustion conditions if a voltage supplied to a sparkplug of an engine cylinder is less than a threshold voltage while thefuel injection flow rate directed to that engine cylinder is greaterthan the threshold fuel injection flow rate. The threshold voltage maycorrespond to a voltage below which a spark is not generated at thespark plug of the engine cylinder. In one example, Q_(inj,TH) may bezero. In another example, engine combustion conditions may be detectedvia crankshaft acceleration increasing above a threshold crankshaftacceleration. The crankshaft acceleration may be measured via acrankshaft position (CKP) sensor such as Hall effect position sensor118. Thus, if the crankshaft acceleration is below the thresholdcrankshaft acceleration, the engine may be determined to be operatingoutside of engine combustion conditions. If the engine is operatingoutside of fuel combustion conditions, such as when the engine is offduring engine shutdown events such as during DFSO, there may be anopportunity for regenerating the exhaust particulate filter since theexhaust gas comprises substantially air or oxygen. In some examples, theexhaust particulate filter may be regenerated during lean air-fuelengine operating conditions. Other examples of engine operation outsideof fuel combustion conditions include during extended engine crankstart-up and during shutdown of the engine.

If the engine is operating outside of fuel combustion conditions at 520,method 500 continues at 522 where the controller 12 may determine if theexhaust particulate filter temperature, T_(PF) is greater than athreshold filter temperature, T_(PF,TH). As described previously,T_(PF,TH) may correspond to a filter temperature above which flowingexhaust oxygen through the exhaust particulate filter may initiatecombustion of soot PM contained therein, thereby regenerating thefilter. As an example T_(PF,TH) may be greater than 450° C., orT_(PF,TH) may include 500° C. When T_(PF)>T_(PF,TH), the exhaustparticulate filter may be preheated and ready for filter regeneration,and the controller 12 may turn off the exhaust particulate filter heater78 at 524 to stop heating the exhaust particulate filter 72. Next,method 500 continues at 526 where the controller 12 may determine if theexhaust particulate filter pressure drop, ΔP_(PF), is greater than athreshold exhaust particulate filter pressure drop, ΔP_(PF,TH).ΔP_(PF,TH) may correspond to a pressure drop above which the exhaustparticulate filter may contain a substantial level of PM therein suchthat ΔP_(PF) may prevent proper exhaust expulsion and reduce engineoperability. If ΔP_(PF)>ΔP_(PF,TH), method 500 continues at 528 wherethe controller 12 may position exhaust diverter valve to direct exhaustgas to the exhaust bypass passage 82 to initiate regeneration of theexhaust particulate filter 72. After 528, method 500 ends.

Returning to 520 for the case where the engine is operating within fuelcombustion conditions, method 500 continues at 530 where controller 12may determine if T_(PF)<T_(PF,TH). If T_(PF)<T_(PF,TH) at either 530 or522, method 500 continues at 534 where the controller 12 switches theexhaust particulate filter heater 78 ON to start heating the exhaustparticulate filter. In this way, the exhaust particulate filter 72 maybe preheated during engine combustion conditions when the engine is warmand PM generation is low. As such, the exhaust particulate filter 72 maybe prepared (e.g., preheated) for regeneration, even during shortperiods of engine ON operation. Next, method 500 continues from 534 orfrom 526 if ΔP_(PF)<ΔP_(PF,TH) at 536 where controller 12 may positionthe exhaust diverter valve 80 to divert exhaust gas to bypass theexhaust particulate filter 72. During fuel combustion and warm engineconditions, PM generation in the engine is reduced and the exhaust gasmay bypass the exhaust particulate filter while the filter is preheatedfor regeneration. Furthermore, outside of fuel combustion conditionswhen ΔP_(PF)<ΔP_(PF,TH), the exhaust particulate filter is in aregenerated state and exhaust gas may be directed to bypass the exhaustparticulate filter.

Returning to 530 for the case where T_(PF)>T_(PF,TH), method 500continues at 538 where the controller 12 switches the exhaustparticulate filter heater OFF to stop heating the exhaust particulatefilter 72. When T_(PF)>T_(PF,TH), the exhaust particulate filter 72 ispreheated and ready for regeneration; further heating of the exhaustparticulate filter 72 may reduce fuel economy unnecessarily. After 538,method 500 continues at 536 where the exhaust diverter valve ispositioned to direct exhaust gas to bypass the exhaust particulatefilter. After 536 method 500 ends.

In this manner, a method for an engine may comprise: during a cold startcondition comprising an engine temperature being less than a thresholdengine temperature, directing engine exhaust gas to an exhaustparticulate filter; and during a warm engine condition, directing engineexhaust gas to bypass the exhaust particulate filter, wherein the warmengine condition comprises the engine temperature being greater than orequal to the threshold engine temperature and fuel being combusted inthe engine. Additionally or alternatively, the method may furthercomprise directing combusted exhaust gas to the exhaust particulatefilter only during the cold start condition. Additionally oralternatively, the method may further comprise heating the exhaustparticulate filter during the warm engine condition. Additionally oralternatively, the method may further comprise stopping heating of theexhaust particulate filter during the cold start condition. Additionallyor alternatively, the method may further comprise directing engineexhaust gas to the exhaust particulate filter during a regenerationcondition, wherein the regeneration condition comprises the enginetemperature being greater than or equal to the threshold enginetemperature and a fuel injection flow rate being less than a thresholdinjection flow rate. Additionally or alternatively, the method mayfurther comprise directing engine exhaust gas to bypass the exhaustparticulate filter during the regeneration condition in response to anexhaust particulate filter pressure drop being less than a thresholdpressure drop. Additionally or alternatively, the method may furthercomprise stopping heating of the exhaust particulate filter during theregeneration condition. Additionally or alternatively, the method mayfurther comprise stopping heating of the exhaust particulate filter inresponse to an exhaust particulate filter temperature being greater thana threshold filter temperature. Additionally or alternatively, themethod may further comprise thermally insulating the exhaust particulatefilter.

In this manner, a method may comprise: in response to an enginetemperature being greater than a threshold engine temperature, directingexhaust gas to bypass an exhaust particulate filter during engine fuelcombustion, and heating the exhaust particulate filter when an exhaustparticulate filter temperature decreases below a threshold filtertemperature; and in response to an engine temperature being less than athreshold engine temperature, directing exhaust gas to the exhaustparticulate filter and stopping the heating of the exhaust particulatefilter. Additionally or alternatively, the method may further comprisein response to the engine temperature being greater than the thresholdengine temperature, directing exhaust gas to the exhaust particulatefilter during deceleration fuel shut-off (DFSO). Additionally oralternatively, the method may further comprise in response to the enginetemperature being greater than the threshold engine temperature and anexhaust particulate filter pressure drop being less than a thresholdpressure drop, directing exhaust gas to bypass the exhaust particulatefilter during DFSO. Additionally or alternatively, the method mayfurther comprise, in response to the exhaust particulate filtertemperature increasing above the threshold filter temperature via theheating, directing uncombusted exhaust gas to regenerate the exhaustparticulate filter

Turning now to FIG. 6, it illustrates a timeline 600 depicting operationof an exhaust system including an exhaust diverter valve 80 and anexhaust particulate filter 72 and exhaust particulate filter heater 78positioned in an exhaust bypass passage 82. Timeline 600 includes trendlines for engine status 604, engine temperature, T_(engine) 610, fuelinjection flow rate, Q_(inj) 620, exhaust particulate filtertemperature, T_(PF) 630, exhaust particulate filter pressure drop,ΔP_(PF) 640, exhaust diverter valve position 650, exhaust particulatefilter heater status 660, and exhaust particulate filter regenerationstatus 670. Also shown in timeline 600 are threshold engine temperature,T_(engine,TH) 612, threshold fuel injection flow rate, Q_(inj,TH) 622,threshold filter temperature, T_(PF,TH) 632, threshold filter pressuredrop, and ΔP_(PF,TH) 642.

At time<time t1, the engine is OFF, T_(engine) is low (e.g., less thanT_(engine,TH)), Q_(inj) is low (less than Q_(inj,TH)), T_(PF)<T_(PH,TH),the exhaust diverter valve is positioned to bypass the exhaustparticulate filter, the exhaust particulate filter heater is OFF, andthe exhaust particulate filter regeneration status is OFF. ΔP_(PF) is ata moderate level greater ΔP_(PF,TH), perhaps due to prior vehicleoperation when the exhaust particulate filter was partially clogged withPM from cold start engine operation. At time t1, the engine is turnedON, Q_(inj) increases above Q_(inj,TH) and the engine temperature beginsto rise, indicating fuel combustion in the engine. In response to theengine being ON and T_(engine)<T_(engine,TH) (e.g., cold startconditions), the controller 12 positions the exhaust diverter valve todivert exhaust gas to the exhaust particulate filter so that PMgenerated by combustion in the cold engine can be filtered from theexhaust passage and PM emissions can be reduced. Consequently, aftertime t1, ΔP_(PF) begins to increase as PM is trapped within the exhaustparticulate filter. As T_(engine) increases, the rate of PM generatedfrom fuel combustion may decrease, however, the rate of increase ofΔP_(PF) may increase in response to the higher levels of PM contained inthe exhaust particulate filter.

At time t2, T_(engine) increases above T_(engine,TH), indicating warmengine conditions. In response, the controller 12 may position theexhaust diverter valve to direct the exhaust gas to bypass the exhaustparticulate filter since PM generation rates from engine combustionduring warm engine conditions may be very low as compared to cold startengine conditions when T_(engine)<T_(engine,TH). Thus, at time t2,ΔP_(PF) ceases to increase since no further PM is being filtered fromthe exhaust gas by the exhaust particulate filter 72. In response toT_(engine)>T_(engine,TH) and in response to Q_(inj)>Q_(inj,TH) (warmengine conditions and fuel combustion conditions), controller 12switches the exhaust particulate filter heater ON to begin preheatingthe exhaust particulate filter to prepare for filter regeneration. Asshown at time t2, T_(PF) begins to increase responsive to the heaterstatus 660 being switched ON.

At time t3, Q_(inj) decreases below Q_(inj,TH), indicating a DFSO orother engine shutdown event outside of engine fuel combustionconditions. Because T_(PF)<T_(PF,TH) between time t3 and time t4, theexhaust particulate filter temperature is not high enough for filterregeneration and controller 12 maintains the exhaust diverter valvepositioned so that exhaust gas bypasses the exhaust particulate filter,and the PF regeneration status remains OFF. At time t4, T_(PF) increasesabove T_(PF,TH), indicating that the exhaust particulate filter ispreheated and ready for filter regeneration. In response to T_(PF)increasing above T_(PF,TH), the controller switches the exhaustparticulate filter heater off, as indicated by the heater statuschanging to OFF at time t4. Because Q_(inj) is greater than Q_(inj,TH)at time t4, the engine is operating within fuel combustion conditionsand the controller 12 maintains the exhaust diverter valve positioned tobypass the exhaust particulate filter.

At time t5, Q_(inj) decreases once again below Q_(inj,TH) indicating aDFSO or engine shutdown event outside of engine fuel combustionconditions. In response to the DFSO event and in response toT_(PF)>T_(PF,TH) and because ΔP_(PF)>ΔP_(PF,TH) (indicating that thefilter contains a substantial level PM that can be regenerated),controller 12 may position exhaust diverter valve to direct the exhaustgas to flow from the main exhaust passage to the exhaust bypass passage82 through exhaust particulate filter 72. Because the engine isoperating outside of fuel combustion conditions at time t5, the exhaustgas may be primarily air or oxygen. The exhaust oxygen flowing throughthe preheated exhaust particulate filter may oxidize and combust the PMcontained therein, thereby regenerating the exhaust particulate filter.

Between time t5 and time t6, T_(PF)>T_(PF,TH), ΔP_(PF)>ΔP_(PF,TH), andQ_(inj) increases above and decreases below Q_(inj,TH) several timesindicating periods of engine operation with and without (e.g., DFSO)fuel combustion. Accordingly, between times t5 and t6, responsive towhen Q_(inj) increases above Q_(inj,TH), the controller 12 positionsexhaust diverter valve to direct exhaust gas to bypass the exhaustparticulate filter and the PF regeneration status is switched OFF.Conversely, between times t5 and t6, responsive to when Q_(inj)decreases below Q_(inj,TH), the controller 12 positions exhaust divertervalve to direct exhaust gas to flow through the exhaust particulatefilter and the PF regeneration status is switched ON. When the PFregeneration status is switched ON, ΔP_(PF) decreases; when the PFregeneration status is switched OFF, ΔP_(PF) stays relatively constantsince exhaust gas is bypassing the exhaust particulate filter.

At time t6, ΔP_(PF) decreases below ΔP_(PF,TH), indicating the filterregeneration is complete (e.g., PM contained in the exhaust particulatefilter have been oxidized and combusted to an extent whereby thepressure drop across the filter due to PM contained therein does notadversely impact exhaust flow). In response, the controller 12 positionsthe exhaust diverter valve to direct exhaust gas to bypass the exhaustparticulate filter and the PF regeneration status is switched OFF.Furthermore, after t6, the PF regeneration status remains off and theexhaust diverter valve remains positioned to direct exhaust gas tobypass the exhaust particulate filter even when Q_(inj) decreases belowQ_(inj,TH) (while T_(PF)>T_(PF,TH) and T_(engine)>T_(engine,TH)) sinceΔP_(PH)<ΔP_(PF,TH).

In this way, the exhaust particulate filter may be reliably regeneratedduring engine shutdown events such as DFSOs while reducing prematurefilter degradation. Furthermore, by avoiding any limiting of the engineshutdown events during filter regeneration, drivability and fuel economymay be maintained. Further still, by diverting the exhaust stream to theexhaust particulate filter during engine cold start conditions andbypassing the exhaust particulate filter during warm engine combustionconditions, the exhaust particulate filter size may be reduced therebylowering manufacturing costs and improving reliability while maintainingvehicle PM emissions.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine, comprising: during a cold start condition comprising an engine temperature being less than a threshold engine temperature, directing engine exhaust gas to an exhaust particulate filter; during a warm engine condition, directing engine exhaust gas to bypass the exhaust particulate filter, wherein the warm engine condition comprises the engine temperature being greater than or equal to the threshold engine temperature and fuel being combusted in the engine, and directing engine exhaust gas to the exhaust particulate filter during a regeneration condition, wherein the regeneration condition comprises the engine temperature being greater than or equal to the threshold engine temperature and a crankshaft acceleration being less than a threshold crankshaft acceleration.
 2. The method of claim 1, further comprising heating the exhaust particulate filter during the warm engine condition, and stopping heating of the exhaust particulate filter during the cold start condition.
 3. The method of claim 2, further comprising directing engine exhaust gas to bypass the exhaust particulate filter during the regeneration condition in response to an exhaust particulate filter pressure drop being less than a threshold pressure drop.
 4. The method of claim 3, further comprising stopping heating of the exhaust particulate filter during the regeneration condition.
 5. The method of claim 4, further comprising stopping heating of the exhaust particulate filter in response to an exhaust particulate filter temperature being greater than a threshold filter temperature.
 6. The method of claim 5, further comprising thermally insulating the exhaust particulate filter.
 7. A method, comprising: in response to an engine temperature being greater than a threshold engine temperature, directing exhaust gas to bypass an exhaust particulate filter during engine fuel combustion, and heating the exhaust particulate filter when an exhaust particulate filter temperature decreases below a threshold filter temperature; in response to the engine temperature being less than the threshold engine temperature, directing exhaust gas to the exhaust particulate filter and stopping the heating of the exhaust particulate filter; and in response to the engine temperature being greater than the threshold engine temperature during deceleration fuel shut-off (DFSO), directing exhaust gas to the exhaust particulate filter.
 8. The method of claim 7, further comprising, in response to the exhaust particulate filter temperature increasing above the threshold filter temperature via the heating, directing uncombusted exhaust gas to regenerate the exhaust particulate filter.
 9. The method of claim 7, further comprising, during a cold start condition comprising the engine temperature being less than the threshold engine temperature, directing exhaust gas to the exhaust particulate filter. 